1. Field of the Invention
The present invention relates generally to a gas turbine engine, and more specifically to a method for testing different internal cooling air passages within an air cooled airfoil such as a rotor blade or a stator vane.
2. Description of the Related Art Including Information Disclosed Under 37 CFR 1.97 and 1.98
In a gas turbine engine, such as a large frame heavy-duty industrial gas turbine (IGT) engine, a hot gas stream generated in a combustor is passed through a turbine to produce mechanical work. The turbine includes one or more rows or stages of stator vanes and rotor blades that react with the hot gas stream in a progressively decreasing temperature. The efficiency of the turbine—and therefore the engine—can be increased by passing a higher temperature gas stream into the turbine. However, the turbine inlet temperature is limited to the material properties of the turbine, especially the first stage vanes and blades, and an amount of cooling capability for these first stage airfoils.
The first stage rotor blade and stator vanes are exposed to the highest gas stream temperatures, with the temperature gradually decreasing as the gas stream passes through the turbine stages. The upper stage airfoils (blades and vanes) must be cooled by passing cooling air through internal cooling passages and discharging the cooling air through film cooling holes to provide a blanket layer of cooling air to protect the hot metal surface from the hot gas stream.
A turbine stator vane can be tested for cooling effectiveness by passing a hot gas stream through the vane while monitoring the pressure differential and the temperature change of the cooling air. Measuring for the inlet pressure and the outlet pressure will provide for the pressure drop through the cooling circuit. Measuring the cooling air temperature entering the cooling circuit and then exiting the cooling circuit will determine the cooling effectiveness of the cooling circuit. This method of testing vane cooling circuits is very expensive if each vane must be cast separately using the standard investment casting technique. For example, an industrial gas turbine engine can have 20 vanes in one stage. If each vane in the stage were designed with a different cooling circuit, the casting tooling for each circuit could cost around $100,000 to produce for testing. The total cost for 20 vanes would be $2 million for the set of vanes.